This invention relates to dental air-polishers which clean by abrading teeth with a soluble abrasive and, in particular, to a control for controlling air flow to an air-polisher handpiece when the polisher is deactivated.
In my co-pending application, Ser. No. 477,609, filed Feb. 9, 1990, I disclosed a control unit for controlling both a scaler and an air-polisher. I have found that when the air polisher is deactivated, such as by the operator's removing his foot from a foot switch which is commonly used to operate dental equipment, some air from the pressurized container of abrasive, together with bleed air, continues to flow through to the air polisher tip. When the unit is operating, the water, which is pressurized, causes the water tubing to expand slightly. When the unit is deactivated, the tubing relaxes, squeezing a small amount of water into the handpiece where it is picked up by the residual air flowing through the handpiece and carried out of the handpiece. This may cause liquid to leak or spritz out of the tip and onto the patient, chair, or whatever is below the handpiece at the time. The spritz that is caused may last up to three or four seconds.
In prior art cleaners, pinch valves have been used to control air flow to the tip. For example, U.S. Pat. No. 3,882,638 to Black uses a pinch valve which cuts off all air flow to the handpiece when the handpiece is not in use. However, the use of a pinch valve is undesirable because, after a while, it creates a set in the abrasive tube which leads to the air-polisher. The set causes a permanent constriction in the tube, and it may even close the tube completely. The reason for the resulting set may be seen in FIG. 4 of European application EP 0,097,288 to Mabille, published Jan. 4, 1984. To avoid this set in the tubing, operators are instructed to move the abrasive tube periodically with respect to the pinch valve.
Some prior art cleaners do not depressurize the abrasive containers prior to closing the valve in the line that leads to the air-polisher handpiece. Examples of such prior art cleaners are the above-noted patents to Black and Mabille. In both of these examples it appears that air is delivered to the container when the pinch valves are closed, except of course, when the units are deactivated. Such a configuration requires that the pinch valve work against the full pressure of the abrasive container.
Further, because the Black patent shuts off all air flow to the handpiece, abrasive and water will remain in the handpiece when it is not in use. As was discussed briefly in my co-pending, co-assigned application U.S. Ser. No. 477,748, filed Feb. 9, 1990, if there is not a continuous supply of air to the tip of the handpiece, remaining abrasive may dry in the tip and clog it. Bleed air is needed to blow the abrasive out of the tip, thereby preventing the tip from clogging.